The Haenyeo, a group of divers from Jeju Korean Island, are recognized for their ability to dive in cold waters without the help of respiratory equipment, even during pregnancy. A study of May 2 at Cell Press Journal Cellular reports It shows that the notable skills of the divers are due to both training and genetic adaptation, including genetic variants associated with cold tolerance and decreased blood pressure. The divers also showed pronounced bradycardia, or deceleration of the heart rate, when they dove, but this trait is probably due to a life of training, not to genetics.
“Haenyeo are incredible, and their incredible skill is written in their genes,” says geneticist Melissa Ilardo of the University of Utah. “The fact that women immerse themselves during their pregnancy, which is really difficult to do, has influenced the people of the entire island.”
The Haenyeo, or “Women of the Sea”, immerse themselves throughout the year in social groups to harvest food for their communities. They begin to train around ten years and continue throughout their lives. Inspired by notable Haenyeo diving skills, researchers wanted to know if they have distinguishable physiological features that help them cope with diving tension, and if so, if these traits are due to genetic adaptation or training.
To find out, the team compared the physiological features and genomes of 30 Haenyeo divers with 30 people not Haenyeo de Jeju, as well as 31 people from Continental Korea. To match the age of the divers, the average age of all participants was 65 years. The researchers compared the heart rate and blood pressure of the resting participants and during the “simulated dives”, where the participants contained their breath while submerged their faces in cold water.
“If you endure your breathing and put your face in a bowl full of cold water, your body responds as if it are diving,” says Ilardo. “Many of the same processes occur in their body that would happen if they went out to the ocean, but it is done in a safe way for people without diving experience.”
The genomic analysis of the team showed that Jeju’s residents, both Haenyeo and Haenyeo, were different from the individuals of Continental Korea, which suggests that all Jeju residents descend from the same ancestral population.
“We can essentially think of everyone, from Jeju as ‘Diving Haenyeo’ or ‘Haenyeo without diving’, because his genetics is the same,” says Ilardo.
The genomic analysis also revealed two genetic variants in the haenyo that can help them cope with the diving pressures, which makes Haenyeo the second known population of traditional breathing divers that has evolved for diving. A gene is associated with cold tolerance, which could make divers less vulnerable to hypothermia. The other gene is associated with a decrease in diastolic blood pressure (that is, blood pressure between cardiac contractions). The variant was found in 33% of Jeju participants but only 7% of continental participants.
“This association can reflect natural selection to mitigate the complications of diastolic hypertension experienced by female divers while immersing itself during pregnancy,” says Ilardo. “Since Bajau’s women also immerse themselves while they are pregnant, we wonder if pregnancy is really driving many of the genetic changes in these diving populations.”
During the simulated immersions, all participants showed diminished heart frequencies, but the cardiac veins of Haenyeo fell significantly more than those of any control group. On average, the cardiac speeds of the divers decreased by 18.8 beats per minute (BPM) compared to a decrease of 12.6 bpm in the non -loop Jeju. A diminished heart rate during diving is beneficial because it saves energy and retains oxygen. Since their genomic analysis indicated that Haenyeo and Jeju without diving are genetically members of the same population, the researchers concluded that this characteristic is probably due to the training of the divers.
“Because the Haenyeo have been diving for a long time, their heart rate has been trained to fall more,” says Ilardo. “This was something we could really see visually: we had a diver whose heart rate fell into more than 40 beats per minute in less than 15 seconds.”
Researchers say that these findings highlight the potential to study traditional diving populations to better understand human genetic and physiological adaptation.
“We are really excited to learn more about how these genetic changes can be affecting the healthy population of Jeju,” says Ilardo. “If we can characterize more deeply how these changes affect physiology, it could inspire the development of therapy to treat different conditions, such as hypertensive disorders of pregnancy and stroke.”
This research was supported by the Naval Research Office, the National Health Institutes and the National Foundation of Sciences.